\So*lid"i*ty\, n. [L. soliditas: cf. F. solidit['e].]
1. The state or quality of being solid; density; consistency,
   -- opposed to {fluidity}; compactness; fullness of matter,
   -- opposed to {openness} or {hollowness}; strength;
   soundness, -- opposed to {weakness} or {instability}; the
   primary quality or affection of matter by which its
   particles exclude or resist all others; hardness;
   massiveness.
         That which hinders the approach of two bodies when
         they are moving one toward another, I call solidity.
                                               --Locke.
2. Moral firmness; soundness; strength; validity; truth;
   certainty; -- as opposed to {weakness} or
   {fallaciousness}; as, the solidity of arguments or
   reasoning; the solidity of principles, triuths, or
   opinions.
3. (Geom.) The solid contents of a body; volume; amount of
   inclosed space.
Syn: Firmness; solidness; hardness; density; compactness;
     strength; soundness; validity; certainty.